Motor vehicle headlight element

ABSTRACT

A motor vehicle headlight element is specified which has at least one light-emitting diode and at least one control apparatus. The control apparatus is suitable for processing a signal which is dependent on a measurement variable and for applying a current corresponding to the signal, to the light-emitting diode. The control apparatus and the light-emitting diode are arranged on a common mount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/DE2005/002154, filed on Nov. 30, 2005, which claims the priority toGerman Patent Application Serial No. 10 2004060890.3, filed on Dec. 17,2004. The contents of both applications are hereby incorporated byreference in their entireties.

FIELD OF THE INVENTION

The invention relates to a motor vehicle headlight element.

BACKGROUND

The documents WO 01/01037 A1 and WO 01/01038 A1 describe a motor vehicleheadlight.

SUMMARY

One object of the present invention is to specify a motor vehicleheadlight element with a particularly long life.

A motor vehicle headlight element is specified.

The motor vehicle headlight element is suitable, for example, foroperation as a light-producing element in a motor vehicle frontheadlight. To this end, a plurality of similar motor vehicle headlightelements can be arranged in one front headlight. It is also possible forthe motor vehicle headlight also to contain other light-producingcomponents, such as halogen lamps or gas-discharge lamps, in addition tothe motor vehicle headlight elements.

According to at least one embodiment of the motor vehicle headlightelement, the motor vehicle headlight element contains at least onelight-emitting diode. The light-emitting diode contains at least onelight-emitting diode chip, and the light-emitting diode preferablycontains a plurality of light-emitting diode chips. The motor vehicleheadlight element is preferably suitable for emission of white light.

In at least one embodiment of the motor vehicle headlight element, themotor vehicle headlight element contains a control apparatus. Thecontrol apparatus is suitable for processing a signal which is dependenton a measurement variable.

The measurement variable may, for example, be a temperature, theintensity with which the light-emitting diode in the motor vehicleheadlight element emits electromagnetic radiation, the ambientbrightness outside the headlight element, the current which is flowingthrough the light-emitting diode, or the like. The measurement variableis detected by a detector and is converted to an electrical signal. Thecontrol apparatus is suitable for processing the electrical signal whichhas been produced as a function of the measurement variable and forapplying a corresponding current to the light-emitting diode. This meansthat the control apparatus controls the current flowing through thelight-emitting diode as a function of at least one physical measurementvariable. The control apparatus may, for example contain amicroprocessor.

According to at least one embodiment of the motor vehicle headlightelement, the control apparatus and the light-emitting diode are arrangedon a common mount. For example, the mount is a printed circuit board.This means that electrical connecting points are arranged on the mount,by means of which, for example electrical contact can be made from theoutside with the control apparatus. Furthermore, the mount preferablyhas electrical conductor tracks, which are suitable for electricallyconnecting the connecting points and the control apparatus, as well asthe control apparatus and the light-emitting diode, to one another. Themount is also preferably used as a heat conduction element and issuitable for emitting the heat that is produced by the light-emittingdiode during operation to, for example a heat sink on which the mount ismounted. According to at least one embodiment of the motor vehicleheadlight element, the motor vehicle headlight element thus has at leastone light-emitting diode.

Furthermore, the motor vehicle headlight element has at least onecontrol apparatus which is suitable for processing a signal which isdependent on a measurement variable and for applying a currentcorresponding to the signal to the light-emitting diode, with thecontrol apparatus and the light-emitting diode being arranged on acommon mount.

According to at least one embodiment of the motor vehicle headlightelement, the control apparatus is suitable for determination of thecurrent through the light-emitting diode as a function of the voltagedrop across a resistor. For this purpose, a shunt resistor is connectedin series with the light-emitting diode. The resistor is preferablyarranged on the mount. With the aid of the voltage drop across the knownresistor, the control apparatus is suitable for determination of thecurrent through the light-emitting diode. The actual value determined inthis way can be compared by the control apparatus with a nominal currentvalue. The control apparatus is then suitable for readjustment of thecurrent through the light-emitting diode in such a way that the currentthrough the light-emitting diode at least approaches the nominal currentvalue.

The nominal current value may for this purpose be predetermined, forexample from outside the motor vehicle headlight element. For thispurpose, an appropriate signal is injected into the control apparatusfrom the outside. By way of example, the signal is injected into thecontrol apparatus by means of a connecting pin, to which the controlapparatus is conductively connected. For this purpose, the connectingpin is preferably arranged on the mount.

The nominal current can be preferably infinitely variable. This allows,for example, infinitely variable dimming of the light-emitting diode byvariation of the nominal current value.

According to at least one embodiment of the motor vehicle headlightelement, this motor vehicle headlight element is suitable for applyingthe current through the light-emitting diode as a function of the signalfrom a temperature sensor. The control apparatus is preferably alsosuitable for provision of a control current for operation of thetemperature sensor.

The temperature sensor produces an electrical signal as a function ofthe temperature of the light-emitting diode. If, for example thetemperature of the light-emitting diode exceeds a predetermined maximumvalue, then the control apparatus is suitable for reduction of thecurrent through the light-emitting diode. The control apparatus is alsosuitable for production of an appropriate fault signal on reaching orexceeding the maximum value. The fault signal may, for example, bepassed to the exterior by means of a connecting pin.

According to at least one embodiment of the motor vehicle headlightelement, the temperature sensor is thermally coupled to thelight-emitting diode. This means that at least a portion of the heatwhich is produced by the light-emitting diode in operation is passed bymeans of thermal coupling from the light-emitting diode to thetemperature sensor. For example, the thermal coupling may be in the formof thermal conduction, thermal radiation or convection. The temperaturesensor is provided, for example by one of the following components: NTCthermistor, PTC thermistor, infrared temperature sensor, diode. Whenusing a diode as a temperature sensor the temperature may be determined,for example by means of the temperature dependency of the forwardvoltage across the diode.

According to at least one embodiment of the motor vehicle headlightelement, the temperature sensor is arranged on the mount. If the mountis a printed circuit board, then the temperature sensor can be connectedto the control apparatus by means of conductor tracks on the printedcircuit board. On the one hand, the signal that is produced by thetemperature sensor can in this way be passed to the control apparatus,on the other hand, the temperature sensor can be supplied with a controlcurrent from the control apparatus.

According to at least one embodiment of the motor vehicle headlightelement, the control apparatus is suitable for application of thecurrent through the light-emitting diode as a function of the signalfrom a photodetector.

The control apparatus is in this case preferably suitable for provisionof a control current for operation of the photodetector. Thephotodetector may, for example be a photodiode or a phototransistor.

According to at least one embodiment of the motor vehicle headlightelement, the photodetector is suitable for detection of theelectromagnetic radiation which is essentially emitted from thelight-emitting diode. The term “electromagnetic radiation which isessentially emitted from the light-emitting diode” in this context meansthat, for example small amounts of scattered light from the outside ofthe motor vehicle headlight element can also strike the photodetector.The photodetector is, however, preferably positioned in such a way thatit detects primarily the electromagnetic radiation emitted from thelight-emitting diode in the motor vehicle headlight element.

For example, it is possible to use the intensity as measured by thephotodetector to determine whether all of the light-emitting diodes inthe motor vehicle headlight element are serviceable. It is also possibleto use the photodetector to determine whether the radiation intensity ofone light-emitting diode has decreased, for example because of ageingphenomena. The current through the light-emitting diode can then beincreased appropriately by the control apparatus. If one light-emittingdiode has failed or the intensity of the electromagnetic radiationemitted from the light-emitting diode has decreased excessively as aresult of ageing phenomena, then the control apparatus is suitable forproduction of a fault signal. By way of example, the fault signal can beemitted to the exterior by means of a connecting pin. The connecting pinis preferably arranged on the mount, for this purpose.

According to at least one embodiment of the motor vehicle headlightelement, the photodetector is arranged on the mount. If the mount is aprinted circuit board, then the photodetector can be connected to thecontrol apparatus via the existing conductor tracks on the printedcircuit board, in order to pass on signals and in order to supply acontrol current to the photodetector.

According to at least one embodiment of the motor vehicle headlightelement, the photodetector is suitable for detecting essentially theambient brightness. The term “essentially the ambient brightness”, inthis case, means that the photodetector is arranged in such a way thatit detects primarily light from outside the headlight element. At most asmall portion of scattered light from the motor vehicle headlightelement strikes the photodetector. For example, an externalphotodetector such as this allows a current to be applied to thelight-emitting diode as a function of the external lighting conditions.If the ambient brightness decreases—for example when driving through atunnel—it is thus possible to increase the current level through thelight-emitting diode. When the ambient brightness increases, the currentlevel can then be reduced again.

The electrical signal which is produced by the photodetector may, forexample, be supplied to the control apparatus by means of a connectingpin. The connecting pin is preferably arranged on the mount for thispurpose. If the mount is a printed circuit board then the connecting pinis connected to the control apparatus by means of conductor tracks onthe printed circuit board.

The motor vehicle headlight element preferably has not only aphotodetector outside the headlight element for detection of the ambientbrightness, but also an internal photodetector for determination of theintensity of the electromagnetic radiation emitted from thelight-emitting diode.

According to at least one embodiment of the motor vehicle headlightelement, the external photodetector is arranged outside the headlight,for example on the motor vehicle car body.

According to at least one embodiment of the motor vehicle headlightelement, at least one varistor is arranged on the mount. The varistor isused, for example, as protection for the components of the motor vehicleheadlight element against overvoltages. For example, the varistorrepresents protection against ESD (electrostatic discharge) voltagepulses.

According to at least one embodiment of the motor vehicle headlightelement, at least one varistor is connected in parallel with thelight-emitting diode. The varistor is then used as ESD protection forthe light-emitting diode in the reverse-biased direction.

According to at least one embodiment of the motor vehicle headlightelement, at least one pi filter is arranged on the mount. The pi filteris used, for example, for radio suppression.

According to at least one embodiment of the motor vehicle headlightelement, a pulse-width modulation circuit is arranged on the mount. Thepulse-width modulation circuit is preferably suitable for dimming thelight-emitting diode. The pulse-width modulation circuit producescurrent at a specific level I₁, for example for a specific time intervalT₁. No current flows through the light-emitting diode (I₂=0) for aspecific time interval T₂. By way of example, the pulse-width modulationproduces an electrical square-wave signal for this purpose. The higherthe duty cycle T₁/(T₁+T₂), the longer the time for which current flowsthrough the light-emitting diode in the time interval T₁+T₂, and thebrighter the light-emitting diode appears to the human user.

The frequency of the pulse-width modulation circuit 1/(T₁+T₂) ispreferably at least 100 Hz, so that the light-emitting diode appears tobe illuminated continuously to the human viewer owing to the inertia ofthe human optical signal processing.

According to at least one embodiment of the motor vehicle headlightelement, the control apparatus is suitable for setting the duty cycle ofthe pulse-width modulation circuit. For example, the control apparatuscan preset a specific duty cycle for the pulse-width modulation circuiton the basis of an external signal which is supplied to the controlapparatus. This allows the light-emitting diode to be dimmed infinitelyvariably, in a preferred manner.

According to at least one embodiment of the motor vehicle headlightelement, a current controlled voltage supply may be arranged on themount. By way of example, the voltage supply may be a step-up/step-downcontroller. A DC/DC converter such as this is preferably suitable forconversion of an external input voltage to a voltage which is suitablefor operation of the light-emitting diode. By way of example, the inputvoltage may be between 6 and 16 V.

The light-emitting diode may be operated, for example with a voltagebetween 1 and 5 V per light-emitting diode chip. The light-emittingdiode is preferably operated with a voltage of about 3.3 V, perlight-emitting diode chip. In the case of a light-emitting diode havingfive light-emitting diode chips by way of example, which are connectedin series, a voltage of about 17 V is applied to the light-emittingdiode.

A flyback converter can also be arranged on the mount, as an alternativeto or an addition to a step-up/step-down controller.

According to at least one embodiment, the control apparatus is suitablefor setting the duty cycle of the DC/DC converter. For example, thelight-emitting diode can thus be dimmed infinitely variably as afunction of an external signal which is supplied to the controlapparatus.

According to at least one embodiment of the motor vehicle headlightelement, at least one connecting pin is arranged on the mount. If themount is a printed circuit board, then the connecting pin is preferablyconnected to the control apparatus via conductor tracks on the printedcircuit board.

According to at least one embodiment, an external electrical signal isinjected into the control apparatus by means of at least one connectingpin.

By way of example, a connecting pin is used to inject into the controlapparatus a signal which presets a nominal current value for the currentlevel flowing through the light-emitting diodes.

Furthermore, a connecting pin can be used to inject into the controlapparatus a signal which is produced by an external detector—for exampleby a photodetector.

Furthermore, a switching signal can be injected into the controlapparatus via a connecting pin. The light-emitting diode in theheadlight element can be switched on and off via the control apparatusby means of the switching signal, that is to say current flows throughthe light-emitting diode, or does not flow through the light-emittingdiode, from the control apparatus as a function of the switching signal.

Furthermore, at least one connecting pin can be arranged on the mount,to which a supply voltage is supplied for operation of the motor vehicleheadlight element. This supply voltage may be DC voltage or AC voltage.If an AC voltage is applied to the connecting pin, then a rectifyingelement is preferably arranged on the mount and is suitable forconversion of the AC voltage to a DC voltage which is suitable foroperation of the light-emitting diode and of the control apparatus.

At least one connecting pin is preferably TTL compatible for incomingsignals.

Furthermore, connecting pins can be arranged on the mount which aresuitable for passing a signal that is produced by the control apparatusto the exterior. For example, when a fault occurs, such as the failureof a light-emitting diode or the overheating of a light-emitting diode,an appropriate signal can be applied to a connecting pin.

All of the connecting pins which are arranged on the mount arepreferably each ESD protected by means of a varistor. The connectingpins are particularly preferably suitable for bus coupling.

According to at least one embodiment of the motor vehicle headlightelement, the light-emitting diode has at least one light-emitting diodechip. The light-emitting diode preferably has a plurality oflight-emitting diode chips. The light-emitting diode chips in thelight-emitting diode may, for example, be connected in parallel or inseries.

The light-emitting diode chip is preferably followed by light-emittingdiode optics. The light-emitting diode particularly preferably has aplurality of light-emitting diode chips, which are followed by commonlight-emitting diode optics. The light-emitting diode optics arepreferably positioned with respect to the light-emitting diode chips insuch a way that the majority of the electromagnetic radiation which isemitted from the light-emitting diode chips is influenced by thelight-emitting diode optics. The light-emitting diode optics preferablycontain at least one of the following optical elements: refractiveoptics, diffractive optics, reflective optics, fibre optics.

According to at least one embodiment of the motor vehicle headlightelement, the light-emitting diode optics are suitable for reducing thedivergence of the light emitted from the light-emitting diode chip. Thismeans that the light emitted from the light-emitting diode chips isinfluenced, for example on passing through the light-emitting diodeoptics, in such a way that its divergence after it emerges is less thanbefore entering the light-emitting diode optics.

In at least one embodiment of the motor vehicle headlight element, thelight-emitting diode optics are in the form of a non-imaging opticalconcentrator. In this case, the light-emitting diode optics arepreferably arranged downstream from the radiation output surface of atleast one light-emitting diode chip in such a way that the radiationinlet opening of the optical element is the actual radiation outletopening of the concentrator. In this way, electro-magnetic radiationwhich enters the light-emitting diode optics through the radiation inletopening leaves the concentrator with less divergence through theradiation outlet opening.

The light-emitting diode optics may be formed at least partiallyaccording to the type of one of the following optical elements: compoundparabolic concentrator (CPC); compound ellyptic concentrator (CEC);compound hyperbolic concentrator (CHC).

The light-emitting diode optics may have reflective side walls which aresuitable for reflection of at least a portion of the electromagneticradiation emitted from the light-emitting diode chip. The side walls arethen at least partially in the form of one of the optical elementsmentioned above.

According to at least one embodiment of the motor vehicle headlightelement, the non-imaging optics concentrator has side walls whichconnect the radiation inlet opening to the radiation outlet opening ofthe light-emitting diode optics and are in this case designed in such away that connecting lines which run on the side walls run essentiallylinearly between the radiation inlet opening and the radiation outletopening. By way of example, the side walls are in this case in the formof a truncated pyramid or a truncated cone.

The light-emitting diode optics may be a solid body composed of adielectric material. The electromagnetic radiation which enters thelight-emitting diode optics through the radiation inlet opening is thenpreferably totally internally reflected on the side boundary surfacesbetween the solid body and the surrounding medium. The light-emittingdiode optics may, however, also be formed by a hollow body whose innerwalls are coated such that they are reflective.

In at least one embodiment of the motor vehicle headlight element, eachlight-emitting diode chip has one and only one associated light-emittingdiode optics element. The radiation inlet opening of the optical elementis in this case preferably arranged downstream from the radiation outputsurface of the light-emitting diode chip, in a main emission directionof the light-emitting diode chip.

However, it is also possible for a plurality of light-emitting diodechips to be associated with one common light-emitting diode opticselement. The light-emitting diode chips may for this purpose bearranged, for example along at least one straight line. The radiationinlet opening of the optical element is then arranged downstream fromthe overall area of the radiation output surfaces of the individuallight-emitting diode chips in one main emission direction of thelight-emitting diode chips.

According to at least one embodiment, the radiation inlet opening of thelight-emitting diode optics has a cross-sectional area which is at mosttwice as large as the total radiation output area of the light-emittingdiode chips which are associated with the optical element. The totalradiation output area is given by the sum of the radiation output areasof the individual light-emitting diode chips which are associated withthe light-emitting diode optics. The area of the radiation inlet openingis preferably at most 1.5, and particularly preferably at most 1.25times the size of the total radiation output area of the light-emittingdiode chips which are associated with the light-emitting diode optics.

With a radiation inlet opening as small as this, the solid angle intowhich the electromagnetic radiation is emitted can be reduced in size asclose as possible to the radiation output area of the light-emittingdiode chip. The cross-sectional area of the conical beam which isemitted from the light-emitting diode chip is particularly small there.This allows components to be designed with optimized etendue. This meansthat a radiation level that is as high as possible is projected onto anarea which is as small as possible. The etendue is a conserved quantityin optics and is formed by the product of the area content of a lightsource and the spatial angle into which the light source emits.

In at least one embodiment of the motor vehicle headlight element, agap, for example an air gap, is arranged between the radiation outputsurface of the light-emitting diode chip and the radiation inlet openingof the light-emitting diode optics.

This means that no particularly divergent radiation enters thelight-emitting diode optics, but can emerge at the side through the gapbefore entering the light-emitting diode optics. This makes it possibleto further reduce the divergence of the electromagnetic radiationemitted from the optical element.

Instead of a gap, it is also possible, for example to form the sidewalls which are arranged downstream from the radiation output surface ofthe light-emitting diode chip in a way, such that they are absorbent ortransparent for electromagnetic radiation close to the radiation inletopening of the optical element. This makes it possible to ensure thatthe highly divergent component of the electromagnetic radiation emittedfrom the light-emitting diode chip does not enter the optical element.

According to at least one embodiment of the motor vehicle headlightelement, the radiation outlet opening of the optical element is followedby an additional optical element in the main emission direction. Theadditional optical element is preferably in the form of light-refractingor light-diffracting optics, making it possible to achieve a furtherreduction in the divergence of the radiation passing through theadditional optical element.

The light-emitting diode optics preferably reduce the divergence of aconical beam passing through the radiation inlet opening at least in onespatial direction in such a way that the conical beam, when it emergesthrough the radiation outlet opening, has a beam angle of between 0 and70°, preferably between 0 and 30°, and particularly preferably between 0and 10° with respect to a longitudinal centre axis of the opticalelement which is at right angle to the radiation output surface of alight-emitting diode chip which is associated with the light-emittingdiode optics.

In at least one embodiment of the motor vehicle headlight element thelight-emitting diode has a luminescence conversion material whichfollows the radiation output surface of at least one of thelight-emitting diode chips. A luminescence conversion materialpreferably follows the radiation output surface of each light-emittingdiode chip in the motor vehicle headlight element.

The luminescence conversion material is preferably suitable forwavelength conversion of at least a portion of the electromagneticradiation emitted from the light-emitting diode chip. The radiationemitted from the light-emitting diode chip is preferably mixed with thecomponent whose wavelength has been converted, to form white light.

However, it is also possible for the electromagnetic radiation emittedfrom the light-emitting diode chip to have its wavelength essentiallycompletely converted by the luminescence conversion material. Forexample, this allows radiation emitted from the light emitting diodechip in the non-visible spectral range to be converted to radiation inthe visible spectral range. Use of two different fluorescent substancesin the luminescence conversion material, for example, makes it possible,for example, to produce white light by light mixing. Suitablefluorescent materials for wavelength conversion are described, forexample, in the document WO 98/12757 whose disclosure content relatingto fluorescent materials is hereby included by back-reference.

The luminescence conversion material may in at least one embodiment ofthe motor vehicle headlight element be added to an at least partiallyradiation-permeable encapsulation compound. The encapsulation compoundpreferably at least partially surrounds the light-emitting diode chip.The encapsulation compound may, for example contain epoxy or siliconematerials.

The luminescence conversion material may, however, also be applied as athin film directly onto the radiation output surface of the individuallight-emitting diode chips.

Furthermore, it is possible for the luminescence conversion material tobe included in the light-emitting diode optics, at least in places. Theluminescence conversion material can thus, for example be applied as athin film to the side walls which are arranged downstream from theradiation output surface of the light-emitting diode chip. Theluminescence conversion material may be distributed homogeneously on theside walls. However, it is possible for the luminescence conversionmaterial to be applied to defined points on the side walls. This allowsparticularly well defined conversion of the electromagnetic radiationpassing through the optical element.

According to at least one embodiment, it is also possible for thelight-emitting diode to contain light-emitting diode chips which emitradiation at different wavelengths. This radiation is then preferablymixed to form white light. For example, the light-emitting diode maycontain at least one light-emitting diode chip which is suitable foremission of light in the red spectral range, at least one light-emittingdiode chip which is suitable for emission of light in the green spectralrange and at least one light-emitting diode chip which is suitable foremission of light in the blue spectral range. In order to improve thecolour reproduction, the light-emitting diode may additionally havelight-emitting diode chips which are suitable for emission of light inother spectral ranges—for example in the yellow spectral range.

According to at least one embodiment of the motor vehicle headlightelement, the motor vehicle headlight element has at least onelight-emitting diode which is suitable for emission of electromagneticradiation in the non-visible spectral range. The light-emitting diode ispreferably suitable for emission of radiation in the infrared spectralrange. For this purpose, by way of example, the light-emitting diode maycontain at least one light-emitting diode chip which is suitable foremission of radiation in the infrared spectral range. The motor vehicleheadlight element is then suitable, for example for use as anillumination device for the traffic area, in conjunction withinfrared-sensitive cameras. Systems such as these may be used innight-vision systems, in sensor systems for pedestrian protection, or asproximity sensor systems for motor vehicles. Illumination by means of aninfrared radiation source in this case offers the particular advantagethat none of those involved in the traffic situation are dazzled, evenwith a relatively high radiation power.

In at least one embodiment of the motor vehicle headlight element atleast one of the light-emitting diode chips in the light-emitting diodehas a radiation output surface through which the majority of theelectromagnetic radiation emitted from the light-emitting diode chip isemitted. All of the radiation which is emitted from the light-emittingdiode chip is particularly preferably emitted through the radiationoutput surface.

The radiation output surface is, for example, provided by a portion ofthe surface of the light-emitting diode chip. The radiation outputsurface is preferably provided by a main surface of the light-emittingdiode chip which, for example is arranged parallel to an epitaxial layersequence of the light-emitting diode chip which is suitable forproduction of electromagnetic radiation.

For this purpose, for example the epitaxial layer sequence may have a pnjunction, a double hetero structure, a single quantum well or,particularly preferably a multiple quantum well structure.

The expression quantum well structure, for the purpose of theapplication, covers any structure in which charge carriers experiencequantization of their energy states by confinement. In particular, theexpression quantum well structure does not include any details about thedimensions of the quantization and thus, inter alia, covers quantumboxes, quantum wires and quantum dots and any combination of thesestructures.

The light-emitting diode chip is preferably a semiconductorlight-emitting diode chip in which the growth substrate has been atleast partially removed and to whose surface facing away from theoriginal growth substrate a mount element is applied. The mount elementcan be chosen relatively freely in comparison to a growth substrate. Amount element is preferably chosen whose thermal coefficient ofexpansion is matched particularly well to the radiation-producingepitaxial layer sequence. Furthermore, the mount element may contain amaterial which is particularly highly thermally conductive.

Light-emitting diode chips such as these which are produced by theremoval of the growth substrate are often referred to as thin-filmlight-emitting diode chips and are preferably distinguished by thefollowing features:

-   -   A reflective layer or layer sequence is applied to or formed on        a first main surface, which faces the mount face of the        radiation-producing epitaxial layer sequence. The reflective        layer or layer sequence reflects at least a portion of the        electromagnetic radiation that is produced in the epitaxial        layer sequence back into this layer sequence.    -   The epitaxial layer sequence preferably has a thickness of at        most 20 μm, and particularly preferably of at most 10 μm.    -   Furthermore, the epitaxial layer sequence preferably contains at        least one semiconductor layer with at least one surface which        has a mixing structure. In the ideal case, this mixing structure        leads to an approximately ergodic distribution of the light in        the epitaxial layer sequence, that is to say it has a stochastic        scattering behaviour which is as ergodic as possible.

One fundamental principle of thin-film light-emitting diode chips isdescribed, for example in the document by I. Schnitzer et al., Appl.Phys. Lett. 63 (16), 18 Oct. 1993, 2174-2176, whose disclosure contentof the fundamental principle of thin-film light-emitting diode chips ishereby included by back-reference.

All of the light-emitting diode chips in the motor vehicle headlightelement are preferably thin-film light-emitting diode chips.

The motor vehicle headlight element described here will be explained inmore detail in the following text using exemplary embodiments and withreference to the associated figures. In the exemplary embodiments andfigures, identical components or components having the same effect arein each case provided with the same reference symbols. The illustratedelements cannot be regarded as being to scale, and in fact individualelements may be illustrated in a highly exaggerated form, in order toassist understanding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic section illustration of a light-emitting diodewith light-emitting diode optics according to a first exemplaryembodiment of the light-emitting diode.

FIG. 2 shows a schematic sketch in order to explain the method ofoperation of a non-imaging optical concentrator.

FIG. 3 shows a section illustration of light-emitting diode opticsaccording to a second exemplary embodiment of the light-emitting diode.

FIG. 4 a shows a schematic view of a first exemplary embodiment of themotor vehicle headlight element described here.

FIG. 4 b shows a perspective view of a second exemplary embodiment ofthe motor vehicle headlight element described here.

FIG. 5 shows a schematic side view of one exemplary embodiment of amotor vehicle headlight with the motor vehicle headlight elementdescribed here.

DETAILED DESCRIPTION

FIG. 1 shows a schematic section illustration of a light-emitting diode20 with light-emitting diode optics 4 according to a first exemplaryembodiment of the light-emitting diode 20.

In this case, the light-emitting diode chip 1 is arranged in a housing2. By way of example the housing 2 may contain a ceramic material. Forexample, the housing 2 has contacts through it in order to make contactwith the light-emitting diode chip 1. In the illustrated exemplaryembodiment, the housing 2 is fitted to a printed circuit board 25. Theprinted circuit board 25 has, for example, conductor tracks and contactpoints for making contact with the light emitting diode chip 1.

The light-emitting diode chip 1 is, for example a thin-filmlight-emitting diode chip, as is explained in the general part of thedescription.

The light-emitting diode chip 1 is followed by light-emitting diodeoptics 4 which may, for example, be a three-dimensional non-imagingoptical concentrator, in the form of a CPC. The light-emitting diodeoptics 4 have a light inlet opening b through which electromagneticradiation 3 emitted from the light-emitting diode chip 1 can pass. Theelectromagnetic radiation 3 is at least partially reflected on the sidewalls of the light-emitting diode optics 4 which, for this purpose, areprovided for example with a reflective coating. The radiation 3 leavesthe light-emitting diode optics through the radiation outlet opening 5.

The closer the radiation inlet opening b of the light-emitting diodeoptics 4 is moved to the radiation output surface of the light-emittingdiode chip 1, the smaller the radiation inlet opening b may be designedto be and the higher is the radiation intensity (etendue) of theelectromagnetic radiation 3 emerging through the radiation outletopening 5. The light-emitting diode optics 4 and the light-emittingdiode chip 1 together form the light-emitting diode 20.

As an alternative to the exemplary embodiment illustrated in FIG. 1, itis possible to arrange a plurality of light-emitting diodes, for examplealong a straight line in the housing 2 and for these light-emittingdiode chips to have common associated light-emitting diode optics 4 (seealso FIG. 4 b).

FIG. 2 shows that the conical beam 6 of the radiation passing throughthe light-emitting diode optics 4 leaves the radiation outlet opening 5at a maximum angle θ with respect to a centre axis 7 of thelight-emitting diode optics 4. The length 1 of the light-emitting diodeoptics 4 in this case governs the angle θ for a given width of theradiation inlet opening b. By way of example, the relationship for anideal compact parabolic concentrator is as follows:

$1 = {\frac{b}{2}\left( {1 + {\sin\;\theta}} \right)\frac{\cos\;\theta}{\sin^{2}\theta}}$

In order to achieve a maximum beam angle of, for example, θ=9°, thelength 1 of the light-emitting diode optics must be approximately 23times as large as the width of the radiation inlet opening b.

FIG. 3 shows that, as an alternative to a CPC-like optical concentrator,the light-emitting diode optics may also have side walls 8 which run instraight lines from the radiation inlet opening b to the radiationoutlet opening 5. In this case, the light-emitting diode optics 4 may bea solid body composed of a dielectric material, whose basic shape is inthe form of a truncated cone or truncated pyramid. In addition, theradiation outlet opening 5 may be curved outwards in the form of aspherical or aspheric lens, which forms an additional light-emittingdiode optics element 9, which is an integral part of the light-emittingdiode optics and is suitable for reducing the divergence of theradiation 3 passing through the optical element 4.

FIG. 4 a shows a schematic plan view of a first exemplary embodiment ofthe motor vehicle headlight element 40 described here.

At least one light-emitting diode 20, as is illustrated by way ofexample in FIG. 1, is in this case arranged on a mount 25. The mount 25is, for example a printed circuit board, for example, a metal coreboard. The mount 25 may, for example, have a base area of at most 30mm×60 mm, preferably of at most 20 mm×40 mm, and particularly preferablyof at most 15 mm×30 mm.

A shunt resistor 12 is connected in series with the light-emittingdiodes 20. The control apparatus 10 can use the voltage drop across theresistor 12 to determine the current which is flowing through thelight-emitting diodes 20. For example, the control apparatus 10 mayinclude an integration circuit in order to determine the current throughthe light-emitting diodes 20.

The current through the light-emitting diodes 20 is set by the controlapparatus 10, on the basis for example of a nominal current value. Thenominal current value may be predetermined for the control apparatus 10by an external electrical signal. The external signal is supplied, forexample by means of the connecting pin 16 d to the control apparatus 10.

Current flows through the light-emitting diodes 20 when an appropriateswitching signal (enable signal) is supplied to the control apparatus10. By way of example, the switching signal may be supplied to thecontrol apparatus 10 by means of a connecting pin 16 c.

Furthermore, the control apparatus 10 may be supplied externally withthe signal from an external photodetector 17 by means of the connectingpin 16 f. The light-emitting diodes 20 then have current passed throughthem by the control apparatus 10 as a function of the ambientbrightness.

The control apparatus 10 may be supplied with signals from aphotodetector 13 and from a temperature sensor 14 as a function ofinternal measurement variables, which are governed essentially by theoperating state of the light-emitting diodes 20.

The temperature sensor 14 is preferably suitable for production of asignal which is dependent on the temperature of the light-emittingdiodes 20. The signal from the temperature sensor 14 is passed to thecontrol apparatus 10, where it is processed. The control apparatus 10then controls the current through the light-emitting diodes 20 as afunction of the signal. If the temperature of the light-emitting diodes20 is too high, for example, then the current flowing through thelight-emitting diodes 20 can be reduced by the control apparatus 10.

The internal photodetector 13 determines the intensity of theelectromagnetic radiation 20 emitted from the light-emitting diodes 20.The signal from the photodetector 13 is passed to the control apparatus10. If the intensity of the light-emitting diodes 20 decreases, forexample because of ageing phenomena, then the current through thelight-emitting diodes 20 can be readjusted appropriately with the aid ofthe control apparatus 10.

Both the temperature sensor 14 and the photodetector 13 are preferablymounted on the mount 25. The temperature sensor may, for example, bethermally coupled to the light-emitting diodes by thermal conduction bymeans of the mount 25. The mount 25 is then used as a thermal conductiveelement. Furthermore, they are electrically connected to the controlapparatus 10 by means of conductor tracks on the mount 25.

In the event of a fault, for example in the event of failure of alight-emitting diode or overheating of the light-emitting diode, thecontrol apparatus 10 can emit an appropriate fault signal to theconnecting pin 16 b.

Furthermore, the control apparatus 10 is suitable for setting anappropriate duty ratio for a controllable voltage supply 11. The controlapparatus 10 can control the current through the light-emitting diodes20 in this way.

By way of example, the control apparatus 10 may have a microprocessor inorder to process the signals arriving at the control apparatus 10. Byway of example, the control apparatus 10 may be a microcontroller.

By way of example, the controllable voltage supply 11 is a DC/DCconverter, which can be operated at a frequency of 100 to 500 kHz.

The controllable voltage supply 11 is suitable for conversion of aninput voltage (which is applied to the connecting pin 16 a by way ofexample) to a voltage which is suitable for operation of thelight-emitting diodes 20.

The motor vehicle headlight element is earthed via the connecting pin 16e.

A varistor (not illustrated) may be connected to earth at all of theconnecting pins 16 a to 16 f, for example as protection againstovervoltages.

Furthermore, as shown on the basis of the example of the connecting pin16 a, a pi filter which may contain a capacitor and an inductance can beconnected in series with the connecting pins 16 a to 16 f. The pi filteris used, for example, for radio suppression.

Furthermore, at least one connecting pin (not illustrated) can bearranged on the mount 25 to form a communication interface, for examplea LIN bus.

FIG. 4 b shows a perspective illustration of a second exemplaryembodiment of the motor vehicle headlight element 40 described here. Inthis exemplary embodiment, a light-emitting diode 20 is arranged on ametal-core board which acts as the mount 25.

By way of example, the light-emitting diode 20 comprises fivelight-emitting diode chips 1. The light-emitting diode chips 1 arearranged, for example, on the base 23 of a housing 2. The housing 2contains, for example a ceramic material. The housing 2 may have innerwalls which are shaped in the form of a non-imaging opticalconcentrator. The inner walls 24 of the housing 2 are preferablydesigned to be reflective, at least in places. The inner walls 24 may befollowed by light-emitting diode optics (not illustrated) in the mainimaging direction of the light-emitting diode chips 1, as has beendescribed further above. The light-emitting diode chips 1 make contactwith inner contact surfaces 21 by means of bonding wires 22. The innercontact surfaces are electrically conductively connected to outercontact surfaces 18, via which electrical contact can be made with thelight-emitting diode.

The mount 25 may also have adjusting holes 26 by which the motor vehicleheadlight element can be adjusted, for example with respect to a mount33.

FIG. 5 shows a schematic section illustration of a headlight with theheadlight elements 40 described here.

A plurality of motor vehicle headlight elements 40 as described in FIGS.4 a and 4 b can in this case be mounted on one mount 33. For example,three motor vehicle headlight elements 40 are mounted on the mount 25.The mount 33 is preferably also used as a heat sink for the heat that isproduced during operation by the light-emitting diodes 20 duringoperation. By way of example, the mount 33 for this purpose has coolingribs on its surface that faces away from the motor vehicle headlightelements 40. The mount 33 preferably contains a highly thermallyconductive metal, such as copper.

The motor vehicle headlight elements 40 and the mount 33 can be adjustedwith respect to one another by means of adjusting pins 32. The motorvehicle headlight elements 40 are also adjusted with respect to oneanother in this way. The adjusting pins 32 may be separate components.The mount 33 and the motor vehicle headlight elements 40 then haverecesses, for example adjusting holes. The adjusting holes on the mount33 and motor vehicle headlight element 40 have a suitable diameter suchthat the adjusting pins 32 are flush with the adjusting holes.

Furthermore, it is possible for the adjusting pins 32 to be an integralcomponent of the mount 33. This means that the adjusting pins aremechanically firmly connected to the mount 33. This can be done, forexample, even during the production of the mount 33. The printed circuitboard 25 for the motor vehicle headlight element 40 then has recesses 26(see FIG. 4 b) which are suitable for holding these adjusting pins.

It is likewise possible for the adjusting pins 32 to be an integralcomponent of the motor vehicle headlight element 40. Recesses forholding these adjusting pins are then provided in the mount 33.

It is also possible for the mount 33 and the motor vehicle headlightelements 40 to be adjusted with respect to one another by means ofadjusting marks. The alignment of the motor vehicle headlight elements40 with respect to the mount 33 and thus also the alignment of the motorvehicle headlight elements 40 with respect to one another can then beachieved, for example, by means of an image processing system. Adjustingmarks are for this purpose located, for example, on the printed circuitboard 25 in the motor vehicle headlight element 40. The adjusting marksmay be recorded by a camera and aligned with respect to a referencepoint, which is located on the mount 33. The reference point may be afurther adjusting mark.

The adjusting marks in the mount 33 and motor vehicle headlight element40 are provided either by markings or specific elements in thecomponents of the headlights. By way of example, specific light-emittingdiode chips 1 in the light-emitting diode 20 may represent adjustingmarks such as these.

By way of example, the motor vehicle headlight elements 40 are followedby a common optical element 30. The optical element 30 is, for example,a diffractive or refractive lens, which follows all of the motor vehicleheadlight elements 40 in the headlight, so that the light which isemitted from all of the light-emitting diodes 20 is influenced by theoptical element 30.

The optical element 30 and the mount 33 are adjusted with respect to oneanother by means of adjusting pins 31. The motor vehicle headlightelements 40 and the optical element 30 are also adjusted with respect toone another in this way.

The adjusting pins may be separate components. However, it is alsopossible for the adjusting pins to be an integral component of the mount33 or of the optical element 30. The other component in each case thenhas recesses—for example adjusting holes—which are suitable for holdingthe adjusting pins.

Preferably after the light-emitting diodes 20 and the mount 33 have beenadjusted and the optical element 30 and the mount 33 have been adjustedwith respect to one another, the motor vehicle headlight elements 40 aremechanically firmly connected to the mount. For example, the motorvehicle headlight elements 40 may be adhesively bonded to the mount 33,screwed or swaged to the mount 33. The optical element 30 is also firmlymechanically connected to the mount 33 preferably after the adjustingprocess.

The invention is not restricted by the description on the basis of theexemplary embodiments. In fact, the invention covers any novel featureas well as any combination of features, which, in particular, includesany combination of features in the patent claims, even if this featureor this combination itself is not explicitly stated in the patent claimsor exemplary embodiments.

LIST OF REFERENCE SYMBOLS

-   1 Light-emitting diode chip-   2 Housing-   3 Radiation-   4 Light-emitting diode optics-   5 Radiation outlet opening-   6 Conical beam-   7 Centre axis-   8 Side walls-   9 Light-emitting diode optics-   10 Control apparatus-   11 Voltage supply-   12 Resistor-   13 Photodetector-   14 Temperature sensor-   15 Pi filter-   16 a-f Connecting pins-   17 Photodetector-   18 Contact surfaces-   20 Light-emitting diode-   21 Contact surfaces-   22 Bonding wires-   23 Base-   24 Inner walls-   25 Mount-   26 Recesses-   30 Optical element-   31 Adjusting pin-   32 Adjusting pin-   33 Mount-   40 Motor vehicle headlight element

1. Motor vehicle headlight element, having at least one light-emittingdiode comprising a plurality of light-emitting diode chips, atemperature sensor thermally coupled to the at least one light-emittingdiode, a common light-emitting diode optics element that follows thelight-emitting diode chips of the at least one light-emitting diode; andat least one control apparatus, which is suitable for processing asignal which is dependent on at least one measurement variable and forapplying a current corresponding to the signal to the at least onelight-emitting diode, wherein the temperature sensor and the at leastone light-emitting diode are arranged on a common mount, and wherein thesignal is dependent on the temperature sensor.
 2. Motor vehicleheadlight element according to claim 1, in which a pi filter is arrangedon the mount.
 3. Motor vehicle headlight element according to claim 1,in which at least one varistor is connected in parallel with the atleast one light-emitting diode.
 4. Motor vehicle headlight elementaccording to claim 1, in which the light-emitting diode optics have aradiation inlet opening which is at most twice as large as a totalradiation output area of the light-emitting diode chips which areassociated with the optical element.
 5. Motor vehicle headlight elementaccording to claim 1, in which the at least one light-emitting diodecomprises at least one thin-film light-emitting diode chip.
 6. Motorvehicle headlight element according to claim 1, in which the motorvehicle headlight element comprises at least one light-emitting diodewhich is suitable for the production of white light.
 7. Motor vehicleheadlight element according to claim 1, in which the control apparatusis suitable for determination of the current through the at least onelight-emitting diode as a function of a voltage drop across a resistor.8. Motor vehicle headlight element according to claim 7, in which theresistor is arranged on the mount.
 9. Motor vehicle headlight elementaccording to claim 1, in which a controllable voltage supply is arrangedon the mount.
 10. Motor vehicle headlight element according to claim 9,in which the control apparatus is suitable for setting a duty cycle ofthe voltage supply.
 11. Motor vehicle headlight element according toclaim 1, in which the motor vehicle headlight element comprises at leastone light-emitting diode which is suitable for production ofelectromagnetic radiation in the non-visible spectral range.
 12. Motorvehicle headlight element according to claim 11, in which the at leastone light-emitting diode is suitable for production of radiation in theinfrared spectral range.
 13. Motor vehicle headlight element accordingto claim 1, in which a pulse-width modulation circuit is arranged on themount.
 14. Motor vehicle headlight element according to claim 13, inwhich the pulse-width modulation circuit is suitable for dimming the atleast one light-emitting diode.
 15. Motor vehicle headlight elementaccording to claim 13, in which the control apparatus is suitable forsetting a duty cycle of the pulse-width modulation circuit.
 16. Motorvehicle headlight element according to claim 1, in which at least oneconnecting pin is arranged on the mount.
 17. Motor vehicle headlightelement according to claim 16, in which the at least one connecting pinis connected in parallel with a varistor.
 18. Motor vehicle headlightelement according to claim 16, in which an external electrical signal isinjected into the control apparatus by means of the at least oneconnecting pin.
 19. Motor vehicle headlight element according to claim1, in which the light-emitting diode optics are suitable for reducing adivergence of electromagnetic radiation emitted from the light-emittingdiode chip.
 20. Motor vehicle headlight element according to claim 19,in which the light-emitting diode optics comprise a non-imaging opticalconcentrator.
 21. Motor vehicle headlight element according to claim 20,in which the light-emitting diode optics are formed at least partiallyaccording to the type of at least one of the following optical elements:CPC, CEC, CHC, truncated pyramid, truncated cone.
 22. Motor vehicleheadlight element according to claim 1, in which the control apparatusis suitable for application of a current to the at least onelight-emitting diode as a function of the signal from a photodetector.23. Motor vehicle headlight element according to claim 22, in which thephotodetector is suitable for detection of the electromagnetic radiationwhich is essentially emitted from the at least one light-emitting diode.24. Motor vehicle headlight element according to claim 23, in which thephotodetector is arranged on the mount.
 25. Motor vehicle headlightelement according to claim 22, in which the photodetector is suitablefor detecting essentially an ambient brightness.
 26. Motor vehicleheadlight element according to claim 25, in which the photodetector isarranged outside the headlight.